Representation and processing of spatial information in lateral occipital cortex

人类有非常复杂的视觉。这种复杂的过程大部分发生在大脑中，那里有大片的皮层专门用于视觉。然而，理解人类大脑如何赋予我们视觉能力仍然是一个重大挑战。功能性磁共振成像（fMRI）提供了一种信息丰富的方法，通过测量将大脑划分为不同的视觉区域，从而获得对这一问题的关注。采用了两种广泛的方法：首先，视觉皮层内的区域根据它们如何对不同类型的刺激作出反应来表征。研究发现，大脑中有选择地对颜色、运动等属性或面部、地点或日常物品等物体类别做出反应的区域。其次，当参与者观看系统地穿过视野的刺激时，记录大脑活动可以确定大脑的哪些部分包含视野的地图。这样的视野图在人类大脑的早期视觉处理阶段很容易被发现，随着技术的改进，很明显，在更高的处理阶段也可以发现更多的视野图。重要的是，一些对特定类型的视觉刺激有选择性反应的区域也包含多个视野地图。因此，这种选择性不太可能来自于在每个组成视野图中执行和复制的神经处理。相反，每个地图将在视觉处理中发挥一个或多个关键作用，并有助于在包含它们的区域中发现类别选择性。然而，到目前为止，关于多重视野图所扮演的处理角色，以及它们对人类视觉感知的贡献，还远远没有完成。这项提议的目的是研究人类大脑的外侧枕区，这是已知的专门用于视觉对象感知。大脑的这个区域也被证明包含6个独立的视野图（LO1-6）。我们提出的工作取决于最近的两个发现。首先，我们希望研究的六幅视野图是最近才被发现的，但我们的实验室是少数能够可靠地识别它们的实验室之一。其次，我们不是仅仅依靠fMRI来探测大脑视觉区域的功能，而是成功地使用经颅磁刺激（TMS）来选择性地破坏两个视野图的处理，并确定了它们在方向和形状感知中的因果作用。综上所述，这些发现为我们提供了独特的能力来评估视野如何映射LO1-6处理和表示视觉信息。我们将确定LO1-6，并使用经颅磁刺激来评估它们在空间视觉中的因果作用。这要求我们测量经颅磁刺激在空间视觉任务中改变视觉表现的方式。我们将确定方向和形状任务的表现是否关键取决于LO1和LO2的处理，但扩展我们之前的工作，看看当方向和形状由不同的属性（如颜色和运动）定义时，情况是否仍然如此。为了进一步评估LO地图在空间视觉中的作用，我们将考虑需要跨大空间尺度整合信息的空间处理，这需要我们组装连贯的线索，这些线索对轮廓和对称性的感知至关重要。TMS实验将由fMRI实验补充，fMRI实验可以在更精细的空间尺度上检查反应，从而可以更仔细地检查较小的LO地图的单独作用。最后，我们将使用可以评估fMRI活动模式的方法来预测参与者所看到的刺激类型，这将使我们能够获得关于视觉信息如何在大脑中呈现以及它如何与我们对日常物体的感知相互关联的新见解。

Humans have a very sophisticated vision. Much of this sophistication lies within the brain where large expanses of cortex are devoted to vision. However, understanding how the human brain endows us with our visual abilities remains a significant challenge. Functional Magnetic Resonance Imaging (fMRI) has provided an informative way in which to gain traction on this issue by yielding measurements that allow the brain to be divided into different visual areas. Two broad approaches have been adopted: Firstly, regions within the visual cortex have been characterised in terms of how they respond to different kinds of stimuli. Research has revealed areas that are selectively responsive to properties such as colour and motion or object categories such as faces, places or everyday objects. Secondly, recording brain activity while participants view stimuli that move systematically through the visual field can determine which parts of the brain contain maps of the visual field. Such visual field maps are easy to detect in the early visual processing stages of the human brain and, as techniques have been refined, it has become clear that many more visual field maps can also be found at higher processing stages. Importantly, some areas that are selectively responsive to specific kinds of visual stimuli also contain multiple maps of the visual field. This selectivity is unlikely therefore to arise from the neural processing that is performed and replicated in each constituent visual field map. Instead, each map will perform one or more crucial roles in visual processing and contribute to the category selectivity found in the regions that encompass them. As yet, however, the account of what processing roles the multiple visual field maps play, and how they contribute to human visual perception, is far from complete. The aim of this proposal is to study the lateral occipital area of the human brain, which is known to be specialised for visual object perception. This area of the brain has also been shown to contain six separate visual field maps (LO1-6). Our proposed work hinges on two very recent findings. Firstly, the six visual field maps that we wish to investigate have only relatively recently been discovered, but our lab is one of only a few that is able to reliably identify them. Secondly, rather than relying on fMRI alone to probe the function of visual areas of the brain, we have successfully used transcranial magnetic stimulation (TMS) to selectively disrupt processing in two of the visual field maps and have determined their causal roles in orientation and shape perception. Taken together, these findings give us the unique capability to evaluate how the visual field maps LO1-6 process and represent visual information.We will identify LO1-6 and use TMS to assess their causal role in spatial vision. This requires that we measure the way TMS changes visual performance in spatial visual tasks. We will determine whether orientation and shape task performance depends crucially on processing in LO1 and LO2, but extend our previous work to see whether this remains the case when orientation and shape are defined by different attributes such as colour and motion. To extend further our assessment of the roles of LO maps in spatial vision we will consider spatial processing that requires integration of information across large spatial scales, which is required for us to assemble coherent cues that are crucial for perception of contours and symmetry. The TMS experiments will be complemented by fMRI experiments that can examine responses at a finer spatial scale allowing the separate roles of the smaller LO maps to be examined closely. Finally, we will use measures that can assess the pattern of fMRI activity to predict the type of stimulus the participant viewed which will allow us to derive new insight about how visual information is represented in the brain and how it interrelates to our perception of everyday objects.